Hi,
I've read that anacharis will work in a betta tank, but my tank is 80 deg F and the anacharis seemed to "cook": it got brown and rotted away. I removed what was left and have it floating in my 75 gallon (temp 76-77 deg F) and so far it has not shown the same signs of decay.

I have some lacy java fern in the betta tank whose leave are also turning brown...I'm wondering if anyone can advise me on WHAT plants will thrive at 80 deg F? I want Mr. Beta Alpha Fish to have a nice, planted tank!

like fish you can acclimate plants to a certain environment. you can get anacharis to become "used" to 80F by slowly bring the temperature up over a few weeks. why do you need that long? because plants take time to grow new leaves that is adapted to a new environment :)
But generally all aquarium plants should do just fine in 80F. anacharis jus happens to be more of a cold water plant...

How new are your plants? Many times, IME, plants will seem to die off when newly added to a tank but then rebound. I have swords, java ferns, anubias, hornwort, anachris, wisteria, etc. in my tanks & my tanks all average 78-80F, sometimes higher depending on the time of year.

Thank you all; the plants were all added about 6 weeks ago, and the tank was already 80 deg F. The only one that didn't get brown was a crypt spiralis, but it didn't grow either so I put it in the 75 gal with two others that are growing beautifully.

So just the lacy java is left, with some dead leaves and some OK ones. I suppose I could turn down the heat in the betta tank, add some new plants, and then slowly raise the temperature back to 80.

I'll take your lists of successful plants to the LFS next time I go, and hope they have some! I'm so ready to be done with plastic plants.